1. Field of the Invention
The present invention relates to electrochemical cells generating electrical energy by means of chemical reactions. More specifically, the invention relates to casings for electrochemical cells, the cells being particularly adapted for powering implantable devices. For that reason, the casings have contoured surfaces to more closely conform to body contours. This facilitates implantation in areas of a body that were heretofore not possible because of geometrical limitations.
2. Prior Art
Recent developments in small electronic devices having various shape and size requirements necessitate comparably small-sized electrochemical cells that are easily manufactured and used in these electronic devices. Preferably, these types of cells are of a high energy density, such as is provided by those predicated on a lithium chemistry. One widely used configuration is to house the high energy density cell in a prismatic-shaped casing 10, as shown in FIG. 1. Whether the cell is of a primary or a secondary chemistry is not important. The casing 10 includes a planar front side wall 12 opposite a planar back side wall (not shown), both of which extend to and meet with a right end wall 14 and an opposed left end wall (not shown). The front and back side walls and the right and left end walls extend to and meet with a planar bottom wall (not shown) in a unitary construction referred to as a deep drawn casing. This unitary casing design has a generally rectangular shape with the front and back side walls being parallel to each other and the right and left end walls being parallel. An alternate construction is to provide individual plates which are connected together as side walls and end walls to form the rectangularly-shaped prismatic casing.
In any event, the connected side walls and end walls form an opening closed by a generally planar lid 16. The lid 16 has a rectangular shape and is welded about its periphery to the upper edges of the respective side walls and end walls. The lid includes a fill opening 18 and a terminal pin opening 20. The fill opening 18 is a port for providing an electrolyte into the casing after an electrochemical couple is housed therein. The port is closed by a closure member, such as a ball 22, sealed therein.
The terminal pin opening 20 supports a glass-to-metal seal comprising a ring of insulative glass 24 surrounding a terminal pin 26 having its interior end (not shown) connected to one of the anode and cathode electrodes housed inside the casing. That way, the terminal pin 26 serves as one of the cell leads. The casing 10, insulated from the terminal pin 26 by the glass-to-metal seal 24, serves as the lead for the other electrode.
The major draw back with the prismatic shaped casing 10 is that it is not necessarily the most optimum or desired shape, for example when the cell is intended to be implanted into a human body, and the like. In such applications, a prismatic shaped housing may not represent the best or most efficient usage of space in the body. According to the present invention, a casing having a contoured shaped is more preferred.
A hybrid casing construction is described in U.S. Pat. No. 5,958,088 to Vu et al. This patent shows a prismatic casing having partially contoured side walls. The cell casing includes opposed major side walls, one having a concave arc while the other has an opposed convex arc. The cell electrodes are disposed within the casing and deflected in a spring like manner to follow the arcs of the opposed side walls. That way, the casing maintains a positive pressure against the cell electrodes. The problem is that while the opposed side walls are arced, the intermediate surrounding end wall does not follow their contours. This makes the Vu et al. casing design impractical for implantation in the human body when a fully contoured shape is most preferred.
Accordingly, there is a need for cells housed in casings having fully contoured side walls more closely matching the shape of the human body than does a prismatic casing.